No matter your relationship status, you never go to bed alone. Nestled within your sheets are countless intruders. For an explanation, we turned to Philip M. Tierno Jr., director of clinical microbiology and immunology at New York University’s Langone Medical Center.

How often should they change their sheets?

Wash sheets and pillowcases once a week, and you’ll eliminate that debris that has accumulated in the bed for that week. You’ll be safer from breathing in that material.

Debris? How can sheets possibly get that dirty?

Human skin cells become food for dust mites. That is one of the biggest problems associated with bedding. Mites accumulate, along with their feces. But there is also animal hair, dander, fungal mold, fungal spores, bodily secretions and bacteria. Also: dust, lint, fibers, particulates, insect parts, pollen, soil, sand and cosmetics.

All this stuff is yucky, but is it a health risk?

It is mainly a threat to respiratory tracts and not an infectious source. If you have allergies or asthma, this matter can exacerbate it. If you don’t have an allergy, you could develop one because you’re constantly challenged.

Is there an ideal way to wash bedding?

The water should be 130 to 150 degrees Fahrenheit, typically the washing machine’s hot-water cycle. Then dry using a hot drying cycle. That is germicidal; it actually kills and destroys a lot of vegetative material. It also kills the dust mites. For extra protection, “bleach is excellent.”

Once a week, hot water. Then I’m safe?

No. To protect the mattress, I use an impervious outer cover. If you look at a mattress, it collects debris by gravity. All kinds of things collect on it that are absorbed into its core. Without the impervious cover, your mattress is a “zoological and botanical garden,” he says.

Can you share other tips for handling and cleaning bed sheets? Feel free to type in your suggestions below!